The Biosphere: biogeochemical cycles

Question 1

Define atom

Answer 1

Smallest unit of a chemical element composed of a nucleus with protons surrounded by electrons

Question 2

Define molecules and compounds

Answer 2

Refer to substances where two or more atoms have combined (e.g. H2) but compounds are where at least two different elements (H2O) combine.

Question 3

Define ions

Answer 3

Atom or molecules that have lost electrons producing a net +ve charge (e.g. H+) are cations whereas atom or molecules that have gained electrons producing a net -ve charge (e.g. O2- ) are anions.

Question 4

Phosphorus cycle

Natural P sources

Answer 4

Natural P sources in some rocks (apatite) and guano (bird

droppings).

Question 5

Phosphorus cycle

P critical to…

Answer 5

Energy metabolism, DNA, animal bones. Is

essential to life.

Question 6

Phosphorus cycle

P in soil ->

Answer 6

P in soil -> soil water -> plants -> organic

molecules -> consumers

Question 7

Phosphorus cycle

How are P distributions explained?

Answer 7

P relatively insoluble but nevertheless water is key to
explaining P distributions.

P mainly adsorbed on to organic/minerogenic particles and moves with them.

Question 8

Nitrogen cycle

Plants use N as a nutrient in form of…

Answer 8

nitrate (NO3− ) and ammonium (NH4+ )

Question 9

Nitrogen cycle

Nitrogen fixation.

Answer 9

Lightning -> O2+ N2 -> NO -> ground as NH4 +.

Biological fixation of N2 to NH4+ is most important source of NH4+ and indirectly NO3− to plants and animals.

Question 10

Nitrogen cycle

Humans perturb the nitrogen cycle in fundamental ways:

Answer 10

• The industrial fixation (Haber–Bosch process-1913) of N2 to ammonium and N-fertilizers (half of all food dependent on N fertilisers)
• The internal combustion engine – NOx emissions
• Animal rearing is associated with the emission of NH3, produced by the decomposition of urine and faeces

Question 11

Nitrogen cycle

Enhanced N-deposition is essentially pollution but it is
also the cause of the “N-fertilization” effect….

Answer 11

• negative effects where ecosystems adapted to limited N, as changes competitive balance
• in surface waters, increased N + P leads to eutrophication and eventual functional decline [not good]
• in other cases, overall plant growth may be enhanced and lead to higher rates of C-uptake (e.g., some forests) [good]
• example of a complex relationship between N and other
  parts of the Earth system and other biogeochemcial cycles

Question 12

Carbon cycle

Molecular organic C

Answer 12

Carbonate CO3-2 (e.g. CaCO3), methane CH4, carbon dioxide CO2, carbon monoxide CO.

Question 13

Carbon cycle

Largest reservoirs

Answer 13

Ocean, terrestrial, atmosphere, (and fossil fuels)

Question 14

Carbon cycle

Key fluxes

Answer 14

Photosynthesis, respiration, decomposition, weathering, volcanic eruptions, fossil fuel combustion

Question 15

Carbon cycle

Atmosphere stock naturally kept in balance by…

Answer 15

Exchanges with land and ocean surface

Question 16

Carbon cycle

Note large size of stocks
relative to fluxes

Answer 16

Atmosphere = one of the smaller stocks

Soils = relatively large stock > vegetation or
surface ocean